The present invention relates to a process for producing insulated electric wires used for wiring in a variety of electronic devices. More particularly, the invention relates to a process for producing a twisted wire having conductors with a thin insulating coating provided by applying insulating paint to the conductors and baking the applied layer.
Insulated wires of a type used for wiring in a large variety of electronic devices are conventionally produced by extruding a covering of insulating material over twisted conductors. Such insulated wires have been used either independently or as conductors for shielded wires, coaxial cables or flat cables.
With the recent tendency to smaller and lighter electronic devices, considerable efforts are being made to further reduce the cross-sectional size of insulated wires, shielded wires and cables. One way of doing this is to reduce the thickness of the insulating coating. It is very difficult, however, to form an adequately thin insulation coating with current extrusion techniques. An alternative that has been proposed is to provide a thin insulating coating by multiple applications and curings of insulating paint. In actual operation, however, problems such as blistering of the coating or entrapment of air bubbles within the coating occur during the steps of applying the isulating paint to the twisted conductors and curing the applied paint. More specifically, when the insulating paint applied to twisted conductors is cured, air left in gaps between twisted conductors, as shown in FIG. 1, will expand as a result of heating to cause blistering in the surface of the coating. This problem can be significantly reduced by baking the applied paint at lower temperatures, for instance, 150.degree. C. or below, but then the coating finally obtained does not harden sufficiently to provide a reliable twisted insulated wire.